Two apparently distinct muscarinic cholinoceptor mechanisms in guinea-pig taenia caecum

Thirty-min treatment of guinea-pig taenia caecum with 300 nM propyl-benzilylcholine mustard (PrBCM) shifted the concentration-response curve for carbachol to the right with a reduction of the maximum contraction, but 90-min treatment did not result in further inhibition. Under these conditions, pilocarpine hardly contracted the preparations, and it competitively antagonized carbachol. Muscarinic agonists might interact with two types of receptor mechanisms and carbachol elicited a stimulus from both types, whereas pilocarpine did so predominantly from the PrBCM-sensitive one.